Progress in computer system development has lead to two inevitable outcomes: ever-faster processing capabilities and ever-larger data storage requirements. To support these features, various data transfer interfaces and associated protocols have been developed. These include interconnects and interfaces that are internal or generally implemented local to a given computer system, such as serial interconnects including Serial ATA, USB (Universal Serial Bus), FireWire, and RapidIO, and PCI Express. External data transfer interconnects and interfaces (targeted for communication both local and remote computing resources) have likewise been developed, including Ethernet, Fibre-Channel, and Synchonous Optical Networks.
An example of a high-speed interface targeted for supporting large and/or distributed data storage in heterogeneous computing environments is InfiniBand. The InfiniBand Architecture (IBA) Specification describes a first order interconnect technology for interconnecting processor nodes and I/O nodes to form a system area network. The architecture is independent of the host operating system (OS) and processor platform. InfiniBand is a switched fabric communications link used in high-performance computing and enterprise data centers. Its features include high throughput, low latency, quality of service and failover, and it is designed to be scalable. The IBA specification defines a connection between processor nodes and high performance I/O nodes such as storage devices.
IBA is designed around a point-to-point, switched I/O fabric, whereby endnode devices (which can range from very inexpensive I/O devices like single chip SCSI or Ethernet adapters to very complex host computers) are interconnected by cascaded switch devices. The physical properties of the IBA interconnect support two predominant environments, with bandwidth, distance and cost optimizations appropriate for these environments:                Module-to-module, as typified by computer systems that support I/O module add-in slots        Chassis-to-chassis, as typified by interconnecting computers, external storage systems, and external LAN/WAN access devices (such as switches, hubs, and routers) in a data-center environment.        
The availability of high-speed interconnects such as Infiniband has facilitated the use of High-Performance Computer (HPC) dusters to perform computational analysis that was previously reserved to supercomputers. Under the HPC cluster approach, thousands of “commodity” computers and/or servers can be interconnected to perform computational analysis in a massively paralleled architecture. Moreover, HPC cluster implementations are often architected to be highly scalable, leading to the potential use of hundreds of thousands or even millions of interconnected computers and/or processing nodes hosted by one or more computers. However, the current InfiniBand architecture specification limits the size of a single InfiniBand subnet to approximately 48,000 nodes. Accordingly, it would be advantageous to support subnets with greater than 48,000 nodes in a way that is compatible with existing InfiniBand software and hardware.